The present disclosure is directed towards a dosing unit (100) for an ambulatory infusion system, including: – a metering pump unit (110), the pump unit including a dosing cylinder (112) and a piston (111), the piston (111) being arranged in sealing sliding engagement inside the dosing cylinder (112) – a valve unit (120), the valve unit (120) having a filling port (127b), the filling port being designed for fluidic coupling with a liquid drug reservoir (300), a draining port (127c), the draining port (127c) being designed for fluidic coupling with an infusion site interface (890), and a shut-off body (126), the shut-off body (126) being movable between a filling position where it fluidic couples the filling port (127b) with the dosing cylinder (112) and an alternative draining position where it fluidic couples the dosing cylinder (112) with the draining port (127c) – a valve driver coupler (125), the valve driver coupler (125) being coupled to or integral with the shut-off body and being the output element of a step switching mechanism. The disclosure is further directed towards a drive unit that may be used in combination with a disclosed dosing unit, an ambulatory infusion system and a method for coupling a dosing unit and a drive unit.La présente invention concerne une unité de dosage (100) pour un système de perfusion ambulatoire, comprenant : - une unité de pompe doseuse (110), lunité de pompe comprenant un cylindre de dosage (112) et un piston (111), le piston (111) étant agencé en association coulissante étanche à lintérieur du cylindre de dosage (112) - une unité de vanne (120), lunité de vanne (120) ayant un orifice de remplissage (127b), lorifice de remplissage étant conçu pour couplage fluidique à un réservoir de médicament liquide (300), un orifice de vidange (127c), lorifice de vidange (127c) étant conçu pour couplage fluidique à une interface de site de perfusion (890), et un corps de fermeture (126), le corps de fermeture (126) étant déplaçable entre
